Case Report: A rare pediatric case of secretory carcinoma of the parotid gland with high-grade components misdiagnosed as pleomorphic adenoma.

BACKGROUND: Secretory carcinoma (SC) of the parotid gland is an extremely rare malignant neoplasm in childhood. Given its close clinical and imaging similarities to pleomorphic adenoma, as well as the high potential for diagnostic inaccuracies in fine-needle aspiration cytology (FNAC), preoperative diagnosis is often clinically challenging. Pediatric patients with salivary gland tumors are frequently misdiagnosed, which may lead to unfavorable clinical consequences.

CASE PRESENTATION: A 12-year-old male presented with an asymptomatic left parotid mass of 6 months' duration. Preoperative fine-needle aspiration cytology was suggestive of pleomorphic adenoma. Magnetic resonance imaging (MRI) demonstrated a well-circumscribed nodule measuring 2.5 cm in maximum diameter. Intraoperative frozen section favored a low-grade malignant salivary gland tumor. The patient underwent superficial parotidectomy with functional neck dissection (levels I-III). Histopathological examination revealed the following characteristic features of the tumor: small, monomorphic epithelial cells with eosinophilic cytoplasm abundant in secretory granules; frequent microcystic or follicular architectures containing secretory material within the cystic lumina. Additionally, localized high-grade morphological features were identified, including solid areas accounting for more than 30%, nuclear enlargement with prominent nucleoli, discernible mitotic figures, and tumor giant cells. Periodic acid-Schiff (PAS) staining revealed positive secretions rich in glycogen and mucin. Immunohistochemically, the tumor cells were positive for CK19, S100, SOX10, and Mammaglobin. No perineural or lymphovascular invasion was identified. Fluorescence in situ hybridization (FISH) confirmed the presence of an ETV6::NTRK3 gene fusion. Postoperative recovery was uneventful. Multidisciplinary team (MDT) discussion concluded that adjuvant therapy was unnecessary. At 29 months of follow-up, the patient remained disease-free with no evidence of recurrence, preserved facial nerve function, and no radiological signs of residual or recurrent disease.

CONCLUSION: We reported a rare case of non-metastatic parotid SC with high-grade components in a child, which was successfully managed by surgical resection alone. Preoperative clinical manifestations, imaging findings, and FNAC collectively suggested a diagnosis of pleomorphic adenoma. Intraoperative frozen section examination indicated a pathological diagnosis of low-grade malignant salivary gland tumor. Thus, comprehensive histopathological and molecular analyses are essential, as the morphological features of this tumor may be deceptively bland.